The long-term aim of this work is to develop effective treatments for progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD). These common neurodegenerative diseases are associated with prominent motor and cognitive abnormalities and have a poor prognosis (median survival 6 - 8 years) because current treatments do not prevent disease progression. Both diseases are characterized by neuronal loss and accumulation of abnormal aggregates of the 4-repeat isoform of the microtubule-associated protein Tau (4R- Tau) in neurons throughout the CNS. It is thought that 4R-Tau is central to the pathogenesis of these disorders: (i) mutations (e.g. P301L) in the MAPT gene encoding Tau can give rise to PSP and CBD phenocopies; (ii) PSP and CBD are strongly associated with genetic variants at the MAPT locus. In order to address a critical barrier to progress in developing drugs to target Tau accumulation and its consequences in neurons in vivo, we propose to develop zebrafish Tauopathy models that are optimized for drug discovery efforts, rapid comparative testing of putative therapeutic agents, and studies to identify novel therapeutic targets. Our preliminary studies showed that transgenic zebrafish expressing a human 4R-Tau transgene in CNS neurons developed progressive neurological phenotypes, brain atrophy, Tau hyperphosphorylation and argyrophilic deposits, similar to the human diseases. In these preliminary studies, transgenic lines with early- onset phenotypes were selected against, because of constitutive transgene expression. In this exploratory proposal, we will employ a conditional expression approach to develop enhanced zebrafish Tauopathy models with phenotypic abnormalities occurring sufficiently early to be maximally useful for drug discovery efforts and comparative efficacy studies in multiwell plate formats. In Aim 1, we will use a bipartite system based on Gal4/UAS to allow expression of 4R-Tau at high levels in CNS neurons, without selecting against the establishment of lines with early-onset phenotypes. We will generate transgenic animals in which WT or P301L mutant human 4R-Tau is expressed under a UAS enhancer, and use novel Gal4 driver lines we have constructed to trans-activate Tau expression widely in the CNS. In Aim 2, we will determine whether zebrafish larvae expressing human Tau conditionally show impaired survival, motor or oculomotor deficits, and whether these phenotypes could be used as drug discovery assays. In Aim 3, we will determine whether zebrafish larvae expressing human Tau conditionally show evidence of Tau hyper-phosphorylation, neurofibrillary tangle formation or neuronal death, and whether this can be imaged in vivo. These novel transgenic lines will be a valuable tool for translational studies to develop new therapies for PSP and CBD, and potentially other Tauopathies such as Alzheimer's disease and chronic head injury. Our future work will exploit these models for drug discovery and development, both early-phase discovery efforts and later optimization studies, to bring new treatments for these disorders into the neurology clinic.